Pharmacokinetics of ASP4345 from Single Ascending-Dose and Multiple Ascending-Dose Phase I Studies

Cognitive impairment is a core feature of schizophrenia. While first- and second-generation antipsychotic drugs treat psychotic exacerbations, no treatment is approved for the cognitive dysfunction. We have identified ASP4345, a positive allosteric modulator of the dopamine type 1 (D₁) receptor that selectively binds to, and enhances the activity of, D₁ receptors. ASP4345 has the potential to be an effective and well-tolerated treatment option for cognitive impairment associated with schizophrenia.

The objective of this study was to determine the pharmacokinetics of ASP4345 in two phase I single ascending-dose and multiple ascending-dose studies.

Both phase I studies were randomized, double blind, and placebo controlled. The single dose-ascending study assessed pharmacokinetics of single oral doses of 3-900 mg of ASP4345 or placebo in the fasted state in healthy adult volunteers. This study also assessed cerebrospinal fluid pharmacokinetics, as well as the effects of food on pharmacokinetic parameters. The multiple ascending-dose study (NCT02720263) assessed the pharmacokinetics of multiple oral doses of 3-150 mg of ASP4345 in patients with schizophrenia or schizoaffective disorder receiving stable antipsychotic drug treatment. The pharmacokinetic data from both studies were summarized using descriptive statistics.

The plasma concentration-time profile in both studies showed a rapid increase in concentrations of ASP4345. The median time to maximum concentration range was 1.00-2.26 h in the single ascending-dose study in the fasted state and 1.25-3.02 h in the multiple ascending-dose study at steady state. There were less than dose-proportional increases in maximum concentration and area under the curve in the single ascending-dose study, where doses had a range from 3 to 900 mg, and in the multiple ascending-dose study in patients with stabilized schizophrenia or schizoaffective disorder, where doses had a range from 3 to 150 mg. The mean terminal elimination half-life was dose independent and had a range from 9.12 to 14.3 h in the single ascending-dose study and from 11.1 to 26.8 h in the multiple ascending-dose study. Additionally, in the single ascending-dose study, absorption of 300 mg of ASP4345 was slightly delayed when administered in the fed state compared with the fasted state; median time to maximum concentration was 1.5 h under the fasting state and 4.0 h under fed states. All other pharmacokinetic parameters were comparable for both conditions. ASP4345 appeared in the cerebrospinal fluid with some delay; time to maximum concentration range was from 2.48 to 7.98 h in cerebrospinal fluid compared with 0.75 to 1.03 h in plasma (median cerebrospinal fluid/plasma = 0.188). The ratio of cerebrospinal fluid to total plasma for area under the curve from 0 to 24 h (0.157-0.573%) and maximum concentration (0.0899-0.311%) and the ratio of cerebrospinal fluid to unbound plasma for maximum concentration (25.0-86.4%) confirm the distribution of ASP4345 into the brain.

The pharmacokinetics of ASP4345 suggest that single daily dosing is appropriate for ASP4345. Furthermore, the concentration of ASP4345 in cerebrospinal fluid compared to free drug concentrations in plasma provides evidence of penetration of ASP4345 into the brain.